Abstract
In this work the authors first summarily describe the main topics that were the subject of their post-graduate activity in fiber sensing at the Applied Optics Group of University of Kent in the late 1980s and early 1990s. After their return to Porto, Portugal, the know-how acquired during their stay at Kent and the collaboration paths that followed between the University of Porto and University of Kent were instrumental in the start-up and progress of optical fiber sensing activity in Portugal. The main topics addressed in this field, the description of some of the relevant developments achieved in recent years, the present situation and the guidelines for the future research and development activity in Portugal in fiber sensing will be the core of this work. © 2011 University of Electronic Science and Technology of China and Springer-Verlag Berlin Heidelberg.

Abstract
The development of an interferometric optical fiber inclinometer is described in this paper. A weak tapered region is induced in a standard single mode fiber in the vicinity of the cleaved fiber tip, using a standard fusion splicer. In this situation an in-fiber Michelson interferometer is constructed that is sensitive to curvature applied in the tapered region. It is shown that depending on the angular range, fringe visibility and/or peak position depend strongly on the applied curvature enabling low cost dielectric inclinometer to be setup that is suitable for high voltage applications. It is presented an analysis of the sensor response by means of experimental measurements and manipulation of these experimental data through computational simulations. The results coming from the numerical simulations indicate a good performance of the sensor within range of angular variation between 3 and 6 degrees and 10 and 14 degrees. A low cost strategy to interrogate the response of sensor using electrically modulated fiber Bragg gratings, a photodetector and frequency analysis is described. The results presented by this electric interrogation technique show a good sensitivity in the range 3.5 to 5.5 degrees.

Abstract
Microstructured optical fibers (MOFs) have been widely studied owing to their potential for obtaining novel transmission, nonlinear and sensing characteristics. Sensing applications of MOFs cover various types of devices for measurements of different physical and specific chemical compounds in gases and liquids employing evanescent field techniques. Such fibers can also be used as active and passive elements in fiber-optic polarimetric and interferometric sensors. We present an in-line fiber modal interferometer fabricated in boron-doped highly birefringent microstructured fiber. The boron-doped region located in the middle of the core decreases the effective index of the fundamental mode and facilitates coupling between the fundamental and the first order mode. The coupling regions have the form of fiber narrowings fabricated using CO2 laser and are distant by a few millimeters. The spectral intensity at the sensor output is modulated only by intermodal interference produced by a short piece of fiber between the two coupling points. Moreover, as the fiber is highly birefringence, each pair of polarization modes produces its own intermodal fringes, which results in the contrast modulation of the overall interference signal observed at the fiber output, and provides an additional degree of freedom to measure simultaneously a pair of measurands.

Abstract
This work describes a large-core air-clad photonic crystal fibre-based sensing structure that is sensitive to refractive index, temperature and strain. The sensing head is based on multimodal interference, and relies on a single mode - large-core air-clad photonic crystal fibre - single mode fibre configuration. Using two distinct large-core air-clad PCF geometries it is possible to obtain an optical spectrum with two dominant loss bands, at wavelengths that have different sensitivities to physical parameters. This characteristic is explored to demonstrate a sensing head that permits the strain-temperature discrimination functionality. It is also shown the large-core air-clad photonic crystal fibre can be applied to implement a sensing head sensitive to the water refractive index changes induced by temperature variations.

Abstract
Optical fibre sensors for Hydrogen detection at low concentrations has become a growing research area using Palladium as an active medium. Palladium is widely used in hydrogen sensing as it show a high and selective affinity for hydrogen. This metal is capable to absorb hydrogen up to 900 times its own volume which permits that during the expansion mechanical forces are applied in the fibre modifying the optical response. Several optical fibre hydrogen sensor heads coated with Palladium are presented and compared using different working principles: interferometric, intensity and fiber grating-based sensors. These principles were applied in Fabry-Perot cavities, fibre Bragg gratings written in fibre SMF28 with etching in the cladding, multimode interferometers and fibre end micro-mirrors. Palladium thin film coatings over the fibre surface and with thicknesses from 10nm to 350nm were produced by using the sputtering RF technique. These studies were performed in a Hydrogen/Nitrogen atmosphere with Hydrogen concentrations from 0% to 4% (lower limit explosion). The Bragg grating inscribed in a fibre with reduced cladding diameter appears to be one of the best approaches for a fibre optic sensing head for Hydrogen detection. Future work will continue the investigation of other fibre optic structures with Hydrogen sensing capabilities and their application in specific field situations will be assessed.

Abstract
A miniature fiber Bragg grating strain rosette is presented. The proposed design is made possible through the development of low curvature radius lossless tapers, thus offering advantages in miniaturization of the rosette configuration. We report on the experimental validation of the miniature rosette design, demonstrating its effective operation.